The present invention relates to imaging devices for generating color images such as digital still cameras, digital video cameras, stand-alone type image scanners, image scanners integrated to copying machines, and the like. More particularly, the present invention relates to an imaging device that uses an imager of the type of that generates an image with color decomposition.
A CCD-type or MOS-type imager (imaging element) for use in digital still cameras or digital video cameras generally has color filters for color decomposition on an imaging surface thereof and captures an image with color decomposition. Thus, each pixel therein provides information about only one color component. Thus, generally conduct color interpolating processing is performed for each of the pixels in the imager for interpolating image information of two other color components, by using the image information of the nearby pixels, such that the image information for all the color components is acquired for each of the pixels in the imager. With this, color pixel data is obtained for all the pixels on the imager.
During the foregoing interpolation processing, other signal processing such as white-balance processing, gamma correction processing, edge enhancement processing, and the like, are generally conducted simultaneously.
The color image data thus processed is generally recorded on a recording medium after compression according to a compression encoding algorithm such as JPEG.
On the other hand, there are cameras that record image date without compression.
Further, there are some high-grade cameras such as single-lens reflex type digital still cameras that have the function or mode of raw-data recording for image data recording. In this raw-data recording mode, the output signal of the imager is recorded on the recording medium after conversion to digital signals (raw image data) without applying data compression.
With regard to the technology of compression of image information obtained by an imager, there is proposed a method and apparatus that uses primary color filters of a Bayer array (see FIG. 2A) in Japanese Laid-Open Patent Application 2002-516540. According to this technology, data compression is applied independently to four signals, i.e., a differential signal of adjacent R and G pixels, a G signal of the G pixel, a differential signal of adjacent B and G pixels, and a G signal of a G pixel.
In the art of digital still cameras and digital video cameras, JPEG or MPEG technology have been used commonly for compression of image data, while JPEG 2000 (ISO/IEC FCD 15444-1) or Motion-JPEG 2000 (ISO/IEC FCD 1544-3) is drawing attention as a new compressive encoding algorithm that can replace the foregoing conventional algorithms.
Meanwhile, it should be noted that the content of the signal processing mentioned above depends on the manufacturer of the imaging device and the details of the processing are usually not disclosed. Thus, in the case a user wishes to conduct a retouch process to the image data according to the object or purpose of generating pictures, or according to the preference of the user, by using a retouch software, it is preferable that the user can use the row image data, which is free from the effect of signal processing that is conducted inside the camera. Further, it is preferable that the effect of the signal processing in the camera does not appear in such a retouch process even in the case that non-reversible compression of image data has been conducted in the camera.
A raw image data recording mode is the mode for meeting the demands of the user. On the other hand, such a row image data recording mode has a drawback in that the amount of the image data to be stored in the recording medium becomes enormous. In case the imager has three million pixels, for example, the image data for a single picture may be several megabytes or more, and the efficiency of using the recording medium is degraded seriously.
In the case of the technology described in the foregoing Japanese Laid-Open Patent Application 2002-516540, op. cit., too, there is conducted a processing for calculating the R-G and B-G difference signals, and thus, problems arise that are similar to the case of signal processing conducted inside the camera as noted above.